On Apr 27, 4:54 pm, n00m <[EMAIL PROTECTED]> wrote: > Another PC, another OS (Linux) and another compiler C++ (g++ 4.0.0-8) > > Compare 2 my latest submissions:http://www.spoj.pl/status/SBANK,zzz/ > > times: 1.32s and 0.60s > > Submitted codes: > > import sys > z=sys.stdin.readlines() > print z[5] > > #include <cstdio> > #include <cstdlib> > #include <vector> > #include <string> > > using namespace std; > > vector<string> vs; > > int main() { > while (true) { > char line[50]; > if (!fgets(line,50,stdin)) break; > vs.push_back(line); > } > return 0; > > } > > If it proves nothing then white is black and good is evil
It seems that the "push_back" line takes most of the time of the code. Remove it and execution will drop to 0.25s. Python readline uses fread instead of fgets: http://svn.python.org/view/python/tags/r251/Objects/fileobject.c?rev=54864&view=markup (see the file_readlines function) If you write a code that does an fread loop, execution will drop to 0.01s. This C code takes 0.25s. Almost all time is spent with string manipulation. #include <stdio.h> #include <string.h> #define B 8192 char vs[100000][40]; char buffer[B]; int main(void) { int count; char *begin, *end; int i; i = 0; while (1) { count = fread(buffer, 1, B, stdin); if (count == 0) break; begin = buffer; while(1) { end = (char *)memchr(begin, '\n', buffer+B-begin); if (end == NULL) { memmove(buffer, begin, buffer+B-begin); break; } memmove(vs[i], begin, end-begin); i = (i+1)%100000; begin = end + 1; } } return 0; } The difference, 0.60s-0.25s = 0.35s is probably mostly python's memory management (which seems to be much more efficient than std::vector default). Very interesting post. :-) I had no idea about how much optimized the builtin library was. -- http://mail.python.org/mailman/listinfo/python-list
